In terms of 2 sonatas, I don't know the Prokofiev that well but I would say that a lot of post romantic sonatas are different to the classical sense of the word (Scriabin and Medtner single movement sonatas come to mind). I would be prepared to be asked why you chose 2 of them, so would thus be inclined to choose something significantly contrasting to a classical sonata.
In terms of Chopin/Prokofiev overplayed. The Scherzo 2 is the culprit in that set so 1 should be ok. Likewise Prokofiev 7 is more overplayed than 3.
I thought specialised areas were more FRSM?
My main advice would be to play to your strengths. If you play all of those well, then great, go for it. If you, for example, only added Prokofiev for a post romantic piece, then you're better off scrapping it for another Baroque/Classical/Romantic work.
I think the difference at LRSM/FRSM is that the performance standard is so high that they expect candidates to play to their strengths rather than satisfy a period requirement. Example, my strength is post 1900 repertoire so were I ever to take the exam I would have some Debussy/Ravel, some Albeniz/Granados and a living composer. Plenty of contrast within the past 112 years, plenty of room to add pieces from an earlier period and biased towards what I play well.
I hope some of that has been helpful